Dengue Virus (DENV) is the most prevalent mosquito-borne virus causing disease in humans, with an estimated 2.5 billion people at risk of DENV infection, resulting in about 390 million annual infections worldwide. There are currently no licensed vaccines or specific therapeutics, and the death rate for severe dengue without proper supportive care can be over 20%. Candidate vaccines being developed by the NIAID utilize live, attenuated DENV strains with a 30 nucleotide deletion (rDEN?30) in the 3' untranslated region (UTR). While viral replication and antibody responses to the NIAID DENV vaccine strains have been well studied in both rhesus macaques and humans, the innate and cellular immune responses remain largely uncharacterized. Based on our preliminary data with rDEN2?30, which show enhanced type I IFN responses in dendritic cells (DCs) and Th1 skewing of CD4+ T cells, we expect to observe differences regarding innate and cellular immune responses induced by WT DENV versus the NIAID vaccine candidates. Our central hypothesis is that the DENV vaccine strains with mutations in the 3' UTR will elicit enhanced host innate immune responses that may lead to more effective antiviral adaptive immune responses. The overall objective of this application is to characterize the cytokine expression profile produced by human DCs and the subsequent T cell priming that occurs in response to infection with NIAID vaccine strains compared to WT DENV strains. We will first address this in human primary cells since there is no reliable animal model that recapitulates dengue disease in humans. Next, we will validate these results in a newly developed, ex vivo human tonsil histoculture system to study DENV infection in the context of whole lymphoid tissue cytoarchitecture. In preliminary studies, we have demonstrated that human tonsil histocultures support a productive infection of WT DENV-2 and rDEN2?30 and support our initial findings in primary cells.